package pool

import "testing"

// TestNewPoolSizes pins NewPool's contract: Len is exactly n, every slot starts
// idle, and Busy is writable by the caller (the pool only owns the bookkeeping).
func TestNewPoolSizes(t *testing.T) {
	zero := NewPool(0)
	if zero.Len() != 0 {
		t.Fatalf("NewPool(0).Len() = %d", zero.Len())
	}
	if zero.IdleIndex() != -1 {
		t.Fatalf("NewPool(0).IdleIndex() = %d", zero.IdleIndex())
	}

	one := NewPool(1)
	if one.Len() != 1 {
		t.Fatalf("NewPool(1).Len() = %d", one.Len())
	}
	if one.Busy[0] {
		t.Fatal("NewPool(1) slot 0 must start idle")
	}
	if one.IdleIndex() != 0 {
		t.Fatalf("NewPool(1).IdleIndex() = %d", one.IdleIndex())
	}

	three := NewPool(3)
	if three.Len() != 3 {
		t.Fatalf("NewPool(3).Len() = %d", three.Len())
	}
	for i := 0; i < 3; i++ {
		if three.Busy[i] {
			t.Fatalf("NewPool(3) slot %d must start idle", i)
		}
	}
}

// TestIdleIndexScanOrder pins that IdleIndex returns the lowest idle index and
// advances as slots are marked busy, then recovers when one is released.
func TestIdleIndexScanOrder(t *testing.T) {
	p := NewPool(3)
	if p.IdleIndex() != 0 {
		t.Fatalf("all idle -> %d, want 0", p.IdleIndex())
	}

	p.Busy[0] = true
	if p.IdleIndex() != 1 {
		t.Fatalf("slot 0 busy -> %d, want 1", p.IdleIndex())
	}

	p.Busy[1] = true
	if p.IdleIndex() != 2 {
		t.Fatalf("slots 0,1 busy -> %d, want 2", p.IdleIndex())
	}

	p.Busy[2] = true
	if p.IdleIndex() != -1 {
		t.Fatalf("all busy -> %d, want -1", p.IdleIndex())
	}

	// Freeing a lower slot wins the scan again.
	p.Busy[1] = false
	if p.IdleIndex() != 1 {
		t.Fatalf("slot 1 freed -> %d, want 1", p.IdleIndex())
	}
}

// TestSingleWorkerBusyFlips covers the 1-worker pool: either the only slot is
// idle (index 0) or the pool reports full (-1).
func TestSingleWorkerBusyFlips(t *testing.T) {
	p := NewPool(1)
	if p.IdleIndex() != 0 {
		t.Fatalf("1 worker idle -> %d, want 0", p.IdleIndex())
	}
	p.Busy[0] = true
	if p.IdleIndex() != -1 {
		t.Fatalf("1 worker busy -> %d, want -1", p.IdleIndex())
	}
	p.Busy[0] = false
	if p.IdleIndex() != 0 {
		t.Fatalf("1 worker released -> %d, want 0", p.IdleIndex())
	}
}